Thread: Top Speed

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If I had a top gear of 0.80 and a rear end gear of a 4.10 what would my top speed be at 6,300 rpm's???? Any one know how to figure this out???? I got me a new used Baby and am trying to figure out what Gear I want to use to run the 1/4 track. Thanks for any help Kurt.

I am trying to figure out if I want to run a 3.73 or a 410 with the top gear of 0.80.
I want a top speed between 160 and 170 MPH. I know with the 3.31 rear gear the top speed
is up around 200 MPH, I'd rather slow the car down from that top speed but I want to get there a little quicker.
Like I said I want my max RPM's at 6,300 to keep my engine safe. The motor was Dyno'd at a little over 800 HP @ 6,300, rear
wheel HP was a little over 700 and the Torque was a little over 660.
This is in a 2009 Shelby GT 500 with a Kennie Bell Super Charger 3.6 and a 5.4 motor.
Thanks again Kurt

Multiply the trans ratio times the rear gear to give you your final drive ratio.

.8 x 3.73 = 2.98

.8 x 4.1 = 3.28

.8 x 3.31 = 2.64

A little rough math based on 170 mph being about 85% of 200 says that you will need around a 3.10 final drive ratio. 3.10 is approximately 15% greater than the 3.31 you have now.

3.10 / .8 = 3.87 rear gear.

Final drive required divided by trans ratio = needed rear gear

So, looks like a 3.90 gear will put you somewhere around your proposed 170 mph top end. That is, provided you can get to 6300 rpm's in top gear.

These answers are all based on percentages, which is all I could do based on the limited amount of info. You need to your tire diameter, at speed, to calculate from gear ratios.

Here's an online calculator that I found, but have never used.

http://www.csgnetwork.com/speedcalc.html

I was rushed to get all that in before leaving for work. A couple of other things come to mind.

First is driveshaft speed. The 20% overdrive at 6300 rpm's will give you slightly over 7500 at the driveshaft. Make sure it's up to it. I'm thinking aluminum DS at the least, but carbon fiber would be better. The stress of even a small imbalance or slight misalignment goes up exponentially as the speed increases.

Second is transmission strength. Torque is what kills transmissions and overdrive will most likely be the weakest gearset. You're looking at around 700 lb. ft. at the crank based on your numbers. Make sure it's up to the task.

A better solution, IMO, is to use a trans that has a direct 1 to 1 lockup (no overdrive) and adjust your rear gear for the desired speed. This will lower DS speed, have less power loss, and most likely be stronger.

Overdrive is for cruising speed economy---not for top end speed---use the gear thats direct 1-1, probably would be 5th????? and carry a lawyer's card next to your drivers license so its easy to find -----------

6300 with a 1:1 tranny, 3.10 rear gear and 28" tires will go 169 mph, not allowing for wind resistance, using the calculator provided by Mike.

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Ya Mike it's a Carbon Fiber Drive line with a 6 speed Manual Trany that's been well with double clutches is what I was told.
I know the Clutch is very smooth and not clanky like my 07 Mustang GT is, and that is factory.
The Factory Super Charger was upgraded from the 2.5 to a 3.6 Kennie Bell.
Pulls like a raped ape and will break the tires loose at just about any speed on cold tires.
Crazy fast.

Ya guys my 5th Gear is 0.80 and my 6th is 0.63.
I gave the 5th gear as my last drag gear.
But of course my 4th gear is 1.00.
The car in this video looks like mine but mine is Black with about the same power.
I could make a simple pulley change and up my power to 2,000 HP, But the factory rod
Bolts would break. So until I pull the pan and change the rod bolts, I'll keep it at 800 HP.
I also have a N Gauge tuner in it as well. Here is the Video.
https://www.youtube.com/watch?v=i91N..._7fidYdGyp_yFI

One thing to consider when changing rod bolts based on conversations with two different machinists. Both told me that when they have done this on LS rods, most of the time they will have one or two rods in a set that will be out of round with ARP bolts versus stock bolts. I was considering this on my engine, but may not for this reason, unless I tear the engine down completely.

I know this has been beat to death on the web, but apparently, there is at least some chance of ruining bearing clearances.

Be careful.

This was the case on the 7.3 I did 2 years ago. I even had to have the mains line bored after we put ARP main studs in it.

The instructions for the ARP 4.6/5.4 modular engine rod bolts say right in it that the rods should always be resized after new bolts are installed. Step #6.

https://cdn.arp-bolts.com/instructions/256-6301.pdf

There is a differance in just screw in bolts (aftermarket rods) and pressed in bolts that use nuts like OEM stuff

plus these days with fractured caps/rods you can't cut down the sides to resize-they will need a bearing that has an oversided external as in foreign and industrial stuff

Ya I know Mike my buddy is a machinist he has been building them 100,000 dollar machines for the desert racers.
Then when they are done with those they have new motor's built and throw those old motors out. Then he takes them
rebuilds them and use's them for drag race motors. Most are better then 1,000 hp naturally aspirated.
He know his stuff, always building the after market blocks for drag racers.
The more I've been looking in to it though the connecting rods are not all that strong and I think I would be a lot
safer to just go to a good aftermarket rod that could stand up to 2,000 hp or so. since all I have to do is a simple pulley
change to up the power.

So just to clear my mind-------you are going to do this in 1/4 mile in a 2009 GT500 with a Kenne Bell blower on a 5.4 engine???

Yes Jerry, I wish it was a VMP super charger but the Kennie Bell is what I have on it now.
The VMP's from what I understand are a lot more aggressive and have a better torque curve.
The good thing is when my Shelby was built the super charger was not water cooled, this Kennie Bell
is water cooled. Plus you can buy another attachment now that is like a Ice bucket that goes in the trunk
and you run lines to the condenser or cooler if you will.
I am also working on some traction issue's since this thing likes to break the tires loose.
It's had some traction stuff done but I need to put on a BMR Watts link and get rid of the 20 inch
rim's and go to like a 15 inch rim if they will fit over the Calipers that are 14's. That way I can put some nice
wrinkle walls on there. It had Nitto's on there but it was breaking those loose too. Wish I could post some photo's
but I have to figure that out yet. I want to keep it street-able though and I still have A/C. LOL!!!!

You'll probably need a high end racing radial. I can't imagine you'll ever to get a 15" to fit over those brakes.